This invention will be described in terms of including high frequency luminance information in a broadcast television signal but is not intended to be limited to this application.
Recently extended definition television (EDTV) systems have been proposed wherein additional picture information is compatibly included in broadcast television signals. Conventional television receivers are not affected by the additional information but special EDTV receivers utilize the additional information to reproduce higher quality images. For example Yoshio Yasumoto et al. in a paper entitled "An Extended Definition Television System Using Quadrature Modulation of the Video Carrier with Inverse Nyquist Filter", (IEEE Transactions on Consumer Electronics, Vol. CE-33, No. 3, Aug. 1987, pp. 173-180) describe a system wherein high frequency luminance signal (4.2-5.2 MHz) is heterodyned to the frequency range of 0.2-1.2 MHz and then used to quadrature modulate the picture carrier. The quadrature modulated carrier is then added to the standard broadcast television signal for transmission. In this arrangement the additional signal is included, at least in part, in the vestigial sideband of the broadcast signal.
Takahiko Fukinuki in U.S. Pat. No. 4,660,072 describes a system for adding high frequency luminance to a broadcast television signal by modulating a carrier having a frequency equal to 1/2 the chrominance subcarrier frequency with the high frequency luminance information. This modulated carrier is added to baseband composite video signal prior to RF modulation for transmission. In this arrangement, the additional signal occupies a frequency range which includes the normal chrominance signal.
In both of the above systems the added signal occupies a frequency range which is detected by conventional receivers, and may tend to introduce artifacts in the reproduced image where the transmission path is less than ideal.
It is an object of the present invention to provide a method and apparatus for including additional information compatibly in a standard video signal with a minimum of interference or artifacts in reproduced images.